a) Field of the Invention
This invention pertains to controlled release pharmaceutical compositions, processes for preparing the compositions, and uses thereof.
b) Description of Related Art
The advent of genetic engineering has resulted in a proliferation of new biopharmaceuticals that are orally inactive and must be administered by subcutaneous injection or intravenous infusion. Considerable effort has been invested in techniques, e.g. passive transdermal delivery, iontophoresis, and permeability enhancement, that have the potential to overcome the barriers presented by natural biological membranes and avoid the trauma of injections. Some successes with nasal, rectal, transdermal and gastrointestinal administration have been achieved with lower molecular weight polypeptides. However, parenteral administration remains the only viable route by which sustained, controlled delivery can be achieved.
The susceptibility of peptides and proteins to proteolysis and rapid clearance from the bloodstream makes them ideal candidates for controlled delivery systems. In addition, due to the high molecular weight and hydrophilicity of proteins, transdermal diffusion is impractically slow. Furthermore, the zero-order delivery kinetics associated with most transdermal systems may not be the optimum kinetic profile because of the potential down-regulation of biological receptors; in many cases pulsed or self-regulated delivery systems may be more efficient and economical.
One class of polymer systems for controlled release of polypeptides is based on polyethylene-co-vinyl acetate (EVA). Langer et al. in Nature 263, pp. 797-800 (1976) have shown that a wide variety of water-soluble macromolecules can be released for weeks and months from thin EVA matrices, formed by suspending macromolecular drug powder in an organic polymer solution and evaporating the solvent. Microscopy of these polymer matrices revealed a two-phase dispersion, with domains of solid drug and polymer matrix. Mechanistic studies have suggested that the macromolecules are released from these devices by a self-diffusion process, i.e. release does not involve dissolution of the drug in EVA or swelling of the polymer bulk, but rather diffusion through aqueous channels and pores created by the dissolution of dispersed macromolecules.
The pioneering work of Kent et al., as disclosed in U.S. Pat. No. 4,675,189, provided for microencapsulation of biologically active substances in polymeric matrices. Since that invention, however, little progress has been made in the development of second generation systems designed to provide controlled release of a variety of active agents.